The present invention relates to circuit breaker latch assemblies and particularly to an improved latch assembly for static trip circuit breakers.
In commonly assigned U.S. Pat. No. 4,001,742, there is disclosed a static trip, three-pole industrial circuit breaker to which the present invention has particular but not necessarily limited application. The latch assembly of this patent disclosure includes interacting primary and secondary latch levers for sustaining the cradle of the breaker operating mechanism in its latched reset position against the bias of charged mechanism springs. As long as this cradle reset position is sustained, the breaker operating mechanism may be articulated such as to motivate the breaker movable contacts to a stable closed circuit position. To then open the breaker contacts, the secondary latch lever is actuated, either manually or automatically via a trip solenoid activated under the control of a static trip unit in response to a sensed overcurrent condition, to release the primary latch lever; the latter then releasing the cradle from its reset position. While this two stage latch assembly arrangement was generally effective, the tolerances imposed on the various latching surfaces were found to be quite stringent and, unless these tolerances were strictly observed, the requisite trip actuating force to be exerted on the secondary latch lever by the trip solenoid became unduly great.
It is accordingly an object of the present invention to provide an improved latch assembly for static trip circuit breakers.
An additional object is to provide a latch assembly of the above character which accommodates less stringent manufacturing tolerances.
A further object is to provide a latch assembly of the above character which accommodates a relatively light trip actuating force.
Yet another object is to provide a latch assembly of the above character which is efficient in construction, economical to manufacture, and reliable in operation.
Other objects of the invention will in part be obvious and in part appear hereinafter.